RU2301834C2 - Method of production of granulated metallic iron - Google Patents

Abstract

FIELD: production of metallic iron in form of granules by means of reduction of raw mixture containing iron oxide, iron ore for example and carbon-containing reductant in furnace with mobile hearth.

SUBSTANCE: amount of CaO-, MgO- and SiO₂-containing agents in the mixture is so adjusted that basicity of slag in form of (CaO+MgO)/SiO₂ is equal to 1.3-2.3. Content of MgO in slag is 5-13 mass-% depending on composition of slag.

EFFECT: low content of sulfur in metallic iron granules.

9 cl, 6 dwg, 4 tbl, 2 ex

Description

Technical field

The invention relates to a method for producing granular metallic iron, in particular to an improved method for efficiently producing high-quality granular metallic iron with high productivity while reducing sulfur concentration to the lowest possible level due to the use of carbon material, such as coal, in accordance with the method according to which the mixture raw material or its compacting, comprising a substance containing iron oxide, such as iron ore or the like, and a carbon-containing reducing agent, such as a carbon material or the like, is subjected to solid-phase reduction by heating in a moving hearth furnace with a reducing atmosphere, whereby the resulting metallic iron is separated from the resulting slag so that the metallic iron obtained is concentrated in the form of particles and solidifies when cooling, after which the production of granular metallic iron is considered complete.

Description of the technical field to which the invention relates

Recently, much attention has been paid to a method for producing granular metallic iron, which is being developed as a relatively small-scale method for producing iron, according to which a mixture comprising an iron oxide-containing substance (source of iron), such as iron ore or the like, and a carbon-containing reducing agent, such as coal or the like, a non-sintered monometallic compact obtained by pressing the aforementioned mixture, or a carbon-containing multilayer compact in the form of pellets, briquettes or the like, rgayut solid phase reduced in the moving hearth furnace with a reducing atmosphere, the obtained metallic iron is separated from the resultant slag and provide the concentration of produced metallic iron, and then cured by cooling the resulting metallic iron, and then obtaining granulated metallic iron is considered complete.

The inventors of the present invention continued to search for an improved method for reducing the amount of sulfur contained in the granular metal iron obtained according to the aforementioned method, which established that substantial desulfurization can be achieved by a method in which a suitable amount of Ca-containing substance exhibits a desulfurizing effect due to the high affinity for sulfur, such as CaCO _3, further added to the raw material mixture including the coal serving ka ETS carbonaceous reductant and an iron oxide-containing, and the above-mentioned raw material mixture is subjected to reduction and melting by heating, while appropriately controlling the heating temperature, the composition of the atmospheric gas, etc. However, the need for further desulfurization is increasing.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a method for producing high-quality granular metallic iron with high productivity and at the same time reducing the sulfur concentration to the lowest possible level, which is the result of producing granular metallic iron using a method according to which a raw material mixture or compact comprising iron oxide substance and carbon-containing reducing agent are heated in a reducing hearth furnace with a reducing atmosphere or the like such that the iron oxide-containing substance undergoes solid-phase reduction with a carbon-containing reducing agent, especially when using coal or the like. as carbon material.

To achieve the above object, using the method for producing granular metallic iron according to the present invention, according to which a mixture of raw materials including an iron oxide-containing substance and a carbon-containing reducing agent is fed to a moving hearth furnace with a reducing atmosphere for heating, the iron oxide contained in the raw material mixtures are reduced with a carbon-containing reducing agent, and the obtained metallic iron is concentrated in the form of particles during their separation from the resulting slag, then the obtained metallic iron is cooled to cure, after which the production of granular metallic iron is considered complete; the amount of CaO-containing substance, MgO-containing substance and SiO ₂ -containing substance contained in the raw material mixture is controlled so that the basicity of the resulting slag (CaO + MgO) / SiO ₂ during the process is from 1.3 to 2.3 and the concentration of MgO is from 5 to 13 wt.% in the composition of the slag and depends on the concentration of each of the components of CaO, MgO and SiO ₂ in the raw material mixture.

According to the aforementioned preparation method according to the present invention, the MgO-containing substance is preferably further mixed with the raw material mixture in such a way as to provide the desired slag basicity and MgO concentration. In most cases, crude dolomite is used as the MgO-containing substance. Moreover, in some cases, the feed mixture preferably additionally contains a suitable amount of CaF ₂ -containing substance, which provides advantages in controlling the flow of the resulting slag. In this case, the concentration of CaF ₂ -containing substance in the feed mixture is preferably from 0.2 to 2 wt.%.

In accordance with the aforementioned method according to the present invention, the carbon-containing powder is preferably fed in such a way that it is distributed over the hearth with a layer of a thickness of 2 mm to 7.5 mm before the raw material mixture is fed into the moving hearth furnace with a reducing atmosphere, while maintaining a high reduction potential in furnaces, due to the action of the aforementioned carbon-containing powder, thereby improving desulfurization and resulting in a granular metallic iron with a low concentration of sulfur As well as increasing the yield of metallic iron. It should be noted that the production process is preferably carried out in a moving hearth furnace with a reducing atmosphere at an operating temperature of from 1250 to 1550 ° C.

Thus, according to the above production method, in which a raw material mixture comprising an iron oxide-containing substance and a carbon-containing reducing agent is subjected to heating and reduction in a moving hearth furnace with a reducing atmosphere, such as a rotary heating hearth furnace with a reducing atmosphere, thus in order to obtain granular metallic iron, a suitable amount of Mg-containing substance as a slag-forming substance is vigorously introduced into said raw material mixture in such a way that both the basicity (CaO + MgO) / SiO _{2 of the} obtained slag and the MgO content relative to the slag composition have suitable ranges of values, inhibiting the increase in sulfur concentration in the obtained granular metallic iron, which inevitably occurs due to the use of coal, coke or the like, used as a carbon material, thereby providing high-quality granular metallic iron containing a small amount of sulfur with high productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a schematic view showing an example of a reducing hearth furnace with a reducing atmosphere used in the method of the present invention;

Figure 2 is a diagram showing the relationship between slag basicity (CaO + MgO) / SiO ₂ and slag melting temperature obtained from tests, in which curve (i) represents a method using only limestone to control slag basicity in a mixture, and the curve (ii) represents a method using both limestone and dolomite;

Figure 3 is a diagram showing the relationship between slag basicity (C + M) / S and slag melting point obtained from other tests, in which curve (i) represents a method using only limestone to control slag basicity in a mixture, and the curve (ii) represents a method using both limestone and dolomite;

4 is a diagram showing the relationship between MgO concentration in slag and sulfur distribution coefficient (S) / [S] when using dolomite to control slag basicity, in which white circles represent test results using iron ore A, and solid circles represent results tests using iron ore B;

5 is a diagram showing the relationship between the slag basicity (C + M) / S and the sulfur distribution coefficient (S) / [S] obtained from the test;

6 is a diagram showing the relationship between the slag basicity (C + M) / S and the sulfur distribution coefficient (S) / [S] obtained from another test.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 is a schematic view showing an example of a reducing hearth furnace with a reducing atmosphere, wherein a rotary hearth furnace is used in accordance with the method of the present invention.

A mixture of materials (in the form of a compacted non-sintered monometallic compact or such a compact as a pellet, briquette or the like) 1, obtained from a substance containing iron oxide, a carbon-containing agent and, if necessary, containing, is loaded into a rotary hearth furnace with a reducing atmosphere 1 CaO, MgO, SiO ₂ or the like, contained in the form of a matrix component or an ash component, in addition, a binder and granular carbon-containing substance 2 are loaded, while loading on a rotating under 4 is carried out continuously through nker 3 for supplying material in such a way as to achieve distribution on the hearth.

More specifically, before loading the mixture of materials 1 through the hopper 3 for loading materials serves powdered carbon-containing material 2 so that it is distributed on the rotating hearth 4, after which serves a mixture of materials 1 so that it covers the above-mentioned powdery carbon-containing material 2. Despite the fact that the description includes a link to an example drawing, according to which a mixture of materials 1 and a carbon-containing substance 2 is fed through a common hopper 3 for loading materials, there is no need It’s possible to say that a device can be used in which a mixture of materials 1 and a carbon-containing substance 2 are fed through two or more bins 3. On the other hand, the supply of carbon-containing substance 2 is so that it is distributed along the hearth, which significantly increases the level desulfurization, as well as the level of recovery, as described below, in some cases may be absent.

Rotating under 4 furnaces A with a reducing atmosphere usually rotates counterclockwise, and the cycle duration is from 8 to 16 minutes depending on operating conditions, while during the cycle the iron oxide contained in the mixture of materials 1 is restored in solid form and concentrated in particles due to a decrease in the melting temperature caused by carburization, as well as the separation of the obtained metallic iron from the resulting slag, after which the production of granular metallic iron for ersheno. It should be noted that furnace A with a reducing atmosphere contains a large number of burners 5 located on the upper side wall and / or ceiling part with respect to the rotating hearth 4 in such a way as to provide under the heat of combustion or heat of radiation from the burners 5.

The mixture of materials 1, fed to a rotary hearth 4 made of refractory material, is heated by the heat of combustion or the heat of radiation from the burners 5 during its rotational movement in a reduction furnace A on a rotary hearth 4, while the iron oxide contained in the mixture of materials 1 , is restored in the solid state, passing through the heating strip in the reduction furnace A, after which the metal iron formed is concentrated in the form of particles, softening due to carburization under the action of tavshegosya carbonaceous reductant, and separating produced metallic iron from molten slag is formed, and then the generated metallic iron is solidified by cooling in the next zone of the rotary hearth 4, after which the generated metallic iron is unloaded from the hearth by using the discharging device 6, such as a screw. It should be noted that the number 7 indicates the channel for the exhaust gas.

On the other hand, a large-sized rotary hearth kiln with a reducing atmosphere, commonly used in practice, is designed in such a way that gaseous fuels, such as natural gas, are burned in a large number of burners located above the rotary hearth so as to provide heat combustion, necessary for the recovery and melting of the mixture of materials supplied to the under. However, an oxidizing gas such as CO ₂ , H ₂ O and the like contained in the exhaust gas resulting from the above-described combustion affects the composition of the atmospheric gas surrounding the mixture of materials, which leads to significant difficulties in maintaining a high atmospheric reduction potential gas, which is (CO + H ₂ ) / (CO + CO ₂ + H ₂ + H ₂ O), in many cases also reduced to CO / (CO + CO ₂ ).

As a result of the reduction of iron oxide contained in the mixture of materials, generally completed on a rotating hearth at the stage of heating and reduction, reduced iron corresponding to pure iron is obtained. Moreover, the reduced iron particles obtained in the heating and reduction step are rapidly carbonized due to the remaining carbon-containing reducing agent contained in the mixture of materials. As a result, their melting point is greatly reduced due to the increased carbon content in the reduced iron, which ensures melting at a predetermined atmosphere temperature (for example, from 1350 to 1500 ° C), as well as the concentration of small particles of reduced iron, while metallic iron is obtained in the form of large granules. At the stage of melting and concentration, the components of the slag contained in the mixture of materials are also subjected to melting and concentration during their separation from metallic iron.

In this case, if the mixture of materials or atmospheric gas surrounding it has a sufficient reduction potential, the sulfur component contained in coal, coke or the like, and acting as a carbon-containing reducing agent added to the mixture of materials, binds as CaS due to the CaO component contained in in the slag, while the sulfur component is separated together with the slag.

However, the authors of the present invention found that if the atmospheric gas has insufficient reduction potential during reduction and melting, then CaS and FeO react, each of which is in equilibrium, which causes the difficulty that the sulfur component is easily absorbed by the molten granular metallic iron to form FeS. Accordingly, the authors of the present invention conducted intensive research to develop a method of maintaining a high level of reduction potential of atmospheric gas surrounding such a mixture of materials.

As a result, the following method was developed. First, a layer of carbon-containing powder is preliminarily loaded onto a sub-furnace with a reducing atmosphere, and then a mixture of materials is used to cover the aforementioned layer of carbon-containing powder (hereinafter referred to as the “layer of carbon-containing powder distributed over the hearth”), followed by heating and reduction. The above method allows you to maintain a high reduction potential of atmospheric gas surrounding such a mixture of materials, as well as to efficiently carry out the reduction and melting reaction for a short period of time from 10 to 16 minutes, which is the period of the rotation cycle of the hearth of the furnace with the reducing atmosphere, thereby relatively improving desulfurization.

However, as described above, the above-described operations carried out in a rotary hearth furnace with a practical reducing atmosphere provide insufficient desulfurization necessary for the stable production of granular metallic iron with a sulfur content of 0.05% or less, and, accordingly, there is a need to develop a way to further confidently reduce the sulfur content in the granular metallic iron. Accordingly, as a result of intensive research, the authors of the present invention have developed a method according to this invention, according to which the slag contains a suitable amount of MgO, and its basicity (CaO + MgO) / SiO ₂ based on the concentration of CaO, MgO and SiO ₂ contained in the mixture materials, are controlled accordingly, providing more effective desulfurization at the stage of reduction and melting, thereby significantly improving the quality of the obtained granular metallic iron.

Specifically, according to this embodiment, the loading amounts of the aforementioned CaO and MgO are controlled in such a way that the basicity of (CaO + MgO) / SiO ₂ slag corresponds to a range of 1.3 to 2.3, and the MgO concentration is from 5 to 13% depending on the type and the amount of the matrix component contained in the iron oxide (iron ore or the like), as well as the type and amount of the ash component contained in the carbon-containing reducing agent (coal, coke powder or the like) contained in the mixture of materials, and Moreover, in some cases, by type and quantity va gangue contained in the CaO-containing substance or MgO-containing substance, which can be added additionally, and the kind and amount of the ash component contained in the carbonaceous powder, which can be loaded so as to be spread over the hearth. This leads to a stable and high desulfurization, thereby ensuring the production of granular metallic iron with a low sulfur content.

It should be noted that to maintain the basicity (CaO + MgO) / SiO _{2 of the} slag component of the charge in the range from 1.3 to 2.3, the amount of CaO-containing substance or MgO-containing substance added separately from the mixture of materials is set based on a matrix component contained in iron ore or the like, loaded as an iron oxide-containing substance, a composition and content of an ash component contained in coal, coke or the like, loaded as a carbon-containing reducing agent, and, moreover, some words teas of the composition and content of the ash component contained in the carbonaceous powder, which can be loaded so as to be spread over the hearth.

Although the types of CaO-containing substance and MgO-containing substance are not particularly limited, in the most general cases, calcium oxide or CaCO ₃ is used as the Ca-containing substance, and the substance obtained from natural ore is preferably used as the MgO-containing substance. , including dolomite or sea water. Moreover, the addition method used in this embodiment is not limited to a specific method, while additional substances can be added to the mixture of materials at the stage of its preliminary preparation, or additional substances are fed to the rotating under previously together or separately from the aforementioned carbon-containing powder supplied by such so as to be distributed over a rotating hearth, or additional substances are added separately from the mixture of materials from the top at the same time or after loading ki mixture of materials, etc.

On the other hand, it was confirmed that the ratio of the sulfur content in the molten slag to the sulfur content in the molten iron (reduced iron), hereinafter referred to as the "sulfur distribution coefficient (S) / [S]", also largely depends on the basicity of the slag, formed upon receipt of metallic iron by known methods. However, despite the fact that the removal of sulfur in the method for producing granular metallic iron using a rotary hearth furnace with a reducing atmosphere according to the present invention is outwardly similar to known methods, its mechanism in the present invention is significantly different from the mechanism of known methods.

In other words, during the distribution of sulfur in the usual production of cast iron or steel, the distribution coefficient of sulfur (S) / [S] depends on its equilibrium, which, in turn, depends on the composition of molten slag on the surface of molten iron, the composition of molten iron and the atmosphere.

On the other hand, in accordance with the method for producing granular metallic iron using a rotary kiln with a reducing atmosphere according to the present invention, the iron oxide in the mixture of materials is reduced using a carbon-containing reducing agent in the solid state at a temperature of about 1250 to 1550 ° C. Thus, iron oxide is deoxidized to produce reduced iron.

Accordingly, most of the coal or coke contained in the mixture of materials is consumed in the solid phase reduction step. On the other hand, while part of the sulfur contained in coal or the like evaporates into the atmosphere, most of it is absorbed by the matrix component or the ash component contained in the mixture of materials, or CaO or the like contained in the added material, which leads to the retention of sulfur in the mixture of materials in the form of CaS.

Moreover, after the completion of the whole solid-phase reduction, the reduced small iron particles in the mixture of materials undergo rapid carburization with the remaining carbon-containing substance, i.e. carbon (C), which, as is clearly shown in the phase diagram of Fe-C, leads to a decrease in the melting point of reduced iron. As a result, it was found that reduced carburized iron melts even at a temperature of, for example, 1500 ° C or less, or even at a temperature of 1350 ° C or less, while small particles of reduced iron are concentrated, which leads to an increase in the particle size of the granular metal gland.

Moreover, at the stage of carburization and the concentration of reduced iron, the components of the slag (metal oxides such as CaO, SiO ₂ , Al ₂ O ₃ , MgO, etc., which were not reduced due to their high degree of affinity with oxygen) are completely or partially melted, and the molten slag that forms is also concentrated, generally ensuring completion of the separation of the slag from the granular metallic iron, concentrated by melting and cementing.

In any case, at the above stage of carburization and the concentration of reduced iron and the resulting slag, the reducing potential of atmospheric gas surrounding the mixture of materials has a strong effect on sulfur (S), mainly bound CaO in the slag with the formation of CaS, even while maintaining the same slag composition. For example, it was confirmed that at a reduction potential of [CO / (CO + CO ₂ )] of atmospheric gas of about 0.7 or less, some or significant amount of sulfur bound as CaS migrates to the reduced iron to form FeS.

Accordingly, in order to reduce the sulfur component (S) contained in the granular metallic iron obtained using the method according to the present invention, i.e. in order to improve actual desulfurization, it is very important to stably hold the sulfur component (S) bound as CaS in the slag in such a way as to prevent the migration of sulfur towards the reduced iron. Accordingly, it is important to maintain the basicity of the slag at the final stage at the highest possible level, as well as maintain a high reduction potential of atmospheric gas.

In the reduction and melting method according to the present invention, iron is preferably not obtained at an atmosphere temperature of 1550 ° C. or more, in contrast to known iron or steel furnaces in which molten iron is reduced in terms of equipment and operation of a rotary furnace with a reducing atmosphere; in this case, iron is preferably obtained at an atmosphere temperature of about 1550 ° C. or less, more preferably at an atmosphere temperature of about 1500 ° C. or less. However, increasing the basicity of the slag formed at the above stage of reduction and melting to a value of 2, 3 or more replaces the concentration of reduced iron, and also increases the melting point of the slag, which slows down the separation of slag. This causes difficulties in obtaining large particles of granular metallic iron in high yield, which is contrary to the purpose of the present invention.

As indicated above, according to this embodiment, the composition of the material is controlled in such a way that the basicity (CaO + MgO) / SiO ₂ ), the designation of which is further reduced to “(C + M) / S”, is in the range from 1.3 to 2,3, while maintaining the concentration of MgO contained in the slag in the range from 5 to 13%, which leads to a significant improvement in the distribution coefficient of sulfur (S) / [S] between the slag and the granular metallic iron obtained at the final stage, and thereby greatly reducing the sulfur content [S] in the granular metallic iron. The grounds for the above-mentioned suitable ranges of slag basicity (C + M) / S and MgO content in the slag are described in detail below.

It should be noted that the fact that the sulfur distribution coefficient (S) / [S] is strongly related to the slag basicity during the interaction between the slag and the metal during the aforementioned conventional production of iron or steel is known. Moreover, it was found that MgO, indispensable in the production method according to the present invention, has a much lower level of desulfurization compared to CaO. According to the present invention, a substantial amount of MgO is used vigorously along with CaO and, as a result, the level of desulfurization in the production method according to the present invention rises sharply compared to a method in which only CaO is used.

Although the reason why a high degree of desulfurization can be obtained by using MgO has not yet been theoretically explained, the following assumption has been made with the test results below. In other words, it has been suggested that the appropriate control of slag basicity (C + M) / S, including a suitable amount of MgO in the resulting slag, provides an optimal manifestation of properties such as melting point, fluidity, or the like. the resulting slag, thereby maximizing the sulfur distribution coefficient (S) / [S] of the resulting slag.

On the other hand, in the production method using a movable hearth melting furnace with a reducing atmosphere according to the present invention, the relationship between the basicity of the slag (C + M) / S formed at the final stage and the melting temperature substantially depends on the type and brand of the substance containing iron oxide ( iron ore or the like) and a carbon-containing reducing agent used as raw materials.

Figure 2, for example, presents the results of a study of the relationship between the basicity (C + M) / S of the resulting slag and the melting temperature in the implementation of the recovery method and melting in a rotary hearth furnace with a reducing atmosphere using a mixture of materials obtained from hematite ore (A) (see table 1 in the example below), which is a typical example of an iron oxide-containing substance, coal (see table 2 in the example below), which serves as a carbon-containing reducing agent, before constituting the main raw material, and further includes limestone used as a CaO-containing substance, and dolomite used as an MgO-containing substance, to obtain the desired basicity of the slag at the final stage.

In the drawings, the melting temperature of the slag is determined based on a phase diagram based on a quaternary system, including CaO, SiO ₂ , Al ₂ O ₃ and MgO, which are the main components of the slag. It should be noted that curve (i) in the drawings represents the relationship between the basicity of the slag and the melting temperature when used as an agent to obtain the desired basicity only limestone, which is a CaO-containing substance. As the curve clearly shows, the basicity of the slag (C + M) / S above about 1.4 causes a sharp increase in the melting temperature of the slag. Moreover, the slag basicity (C + M) / S of about 1.75 raises the melting point of the slag to approximately 1550 ° C, which is considered the maximum possible temperature for an actual practical operation. Moreover, a slag basicity (C + M) / S in excess of about 1.75 causes an increase in the melting temperature of the slag to a level above 1550 ° C, which is outside the range acceptable for the production method according to the present invention. Accordingly, while maintaining the temperature of the atmosphere, the melting and concentration of the resulting slag slows down, making it difficult to concentrate the reduced iron, which impedes the achievement of the objective of the present invention. There is no need to recall that the preparation carried out at an elevated temperature of the atmosphere (operating temperature) exceeding 1550 ° C ensures the melting of slag with high basicity. However, when using a moving hearth furnace according to the present invention, obtaining at an operating temperature of 1550 ° C. or more leads to a significant reduction in its service life due to the nature of the equipment that cannot withstand such a regime.

On the other hand, curve (ii) shown in Figure 2 shows the relationship between the slag basicity (C + M) / S and the melting point when both limestone and dolomite are used as agents to obtain the desired basicity. As is evident from the curve, an increase in the MgO content in the slag at the final stage causes a decrease in the melting point of the slag at the final stage in the entire range of slag basicity compared to curve (i). Moreover, it should be noted that adding a suitable amount of MgO-containing substance to the mixture of materials reduces the melting point of the slag at the final stage to 1550 ° C or less even when the basicity (C + M) / S of the slag is increased to a value of about 2.3, thereby providing the possibility of obtaining without difficulty at an atmosphere temperature of 1550 ° C, causing difficulties in the case shown in figure 1.

As described above, using the production method according to the present invention, the preparation is carried out in a movable hearth furnace of a practical scale with increased basicity (C + M) / S of slag to a value of about 2.3, which is the maximum allowable basicity using an MgO-containing substance in as a basicity regulating agent, providing slag melting at temperatures up to 1550 ° C, suitable for practical production, thereby contributing to the stable production of granular metallic iron in a stable production conditions, while maintaining the distribution coefficient of sulfur (S) / [S] between the slag and the metal at a level of about 25 or more, preferably 35 or more. As a result, granular metallic iron can be obtained at the final stage in a reliable way with a sulfur content of 0.05% or less, preferably with a sulfur content of 0.04% or less, which to some extent depends on the brand of coal or the like, supplied to as a carbon-containing reducing agent, or from a material supplied in such a way as to be distributed across the hearth.

In particular, the production method according to the present invention has the significant advantage of preventing a decrease in the sulfur distribution coefficient (S) / [S] due to the deterioration of the reduction potential of atmospheric gas by controlling the basicity of the slag (C + M) / S and the MgO content, which is inevitable occurs when using the method of heating by combustion using gas burners, most often used for heating in an oven.

It should be noted that a further increase in the ratio in the loading of limestone and dolomite, serving as agents for regulating basicity, further increasing the MgO content in the slag at the final stage, further reducing the melting temperature of the slag at the final stage, may require the use of a device in which basicity of slag (C + M) / S more than 2.3. However, in this case, an excessive increase in the basicity (C + M) / S of the resulting slag increases the viscosity (which causes low fluidity), which slows down the concentration of reduced iron and decreases the yield of granular metallic iron, as well as difficulties in obtaining a suitable granular metallic iron in the form of balls . Accordingly, the maximum basicity value (C + M) / S for this embodiment according to the present invention should be 2.3.

It should be noted that the reason why the minimum basicity value (C + M) / S should be 1.3 is that slag with a basicity lower than the aforementioned minimum value causes a decrease in desulfurization, which leads to difficulties in reducing the sulfur content in the reduced iron, even with a high reduction potential. Accordingly, the slag basicity (C + M) / S for this embodiment according to the present invention should be from 1.4 to 2.0.

Figure 3 shows the relationship between the basicity of the slag (C + M) / S and the melting point of the slag, while the basicity of the resulting slag (C + M) / S is controlled by adjusting the amount of CaO-containing substance and MgO-containing substance added to the mixture of materials mainly consisting of magnetite ore serving as an iron oxide-containing substance and coal serving as a carbon-containing reducing agent shown in Table 2 below in the same manner as in FIG. 2 above.

Despite the fact that the relationship between them depends on the grade of ore, when using only limestone as the basicity regulating agent, as is evident from curve (i) in the drawing, the basicity of slag (C + M) / S of about 1.5 or less provides a melting point slag 1550 ° C. On the other hand, when 32% of limestone is replaced with dolomite in order to control slag basicity, as is evident from curve (ii), an increase in MgO content in slag prevents a rapid increase in the melting temperature due to an increase in slag basicity. For example, even if the basicity of the slag (C + M) / S is increased to a value of about 1.8 or less, the melting point of the slag decreases to the level of 1550 ° C or less.

Figure 4 presents the results of a study of the relationship between the MgO content in the slag and the sulfur distribution coefficient (S) / [S] obtained using the production method according to the present invention. As clearly follows from the drawing, there is a strong relationship between the MgO content in the slag and the sulfur distribution coefficient (S) / [S]. In addition, it is obvious that the sulfur distribution coefficient (S) / [S] does not increase in proportion to the increase in MgO content in the slag, and the sulfur distribution coefficient has a maximum value for a specific range of MgO content in the slag.

In other words, figure 4 presents the test results of two types of mixtures of materials using iron ore A and iron ore B, respectively, used as substances containing iron oxide. Despite the fact that the test results are slightly different due to the properties of the material, the results obtained are generally of the same nature. In any case, the sulfur distribution coefficient (S) / [S] has a high value of 25 or more, and the MgO content is in the range of 5 to 13%, thereby showing the advantage of reducing the sulfur content of the reduced iron. Although the detailed mechanism has not yet been clarified, it is assumed that the slag contained in the feed material in a complex way affects the sulfur distribution coefficient (S) / [S]. In any case, a suitable MgO content in the slag should be in the range of 5 to 13% so as to affect a sulfur distribution coefficient (S) / [S] of 25 or more, based on the test results of these typical two types of iron ore ( A) and (B).

As indicated above, using the method according to the present invention, the basicity of the slag (C + M) / S, established on the basis of the composition of the slag contained in all the raw materials used, and the MgO content in the slag are respectively adjusted so as to ensure the desired melting point of the formed slag and the sulfur distribution coefficient (S) / [S] in the iron oxide-containing substance, the carbon-containing reducing agent, and the like used in this production method.

On the other hand, with a relatively high slag basicity (C + M) / S of 1.8 or more, the interaction is basic, i.e. the increased basicity of the slag (C + M) / S causes a gradual decrease in the concentration of small particles of reduced iron formed due to the substance containing iron oxide, which is reduced in the mixture of materials even if the basicity of the slag (C + M) / S is 2.3 or less.

Moreover, a slag basicity (C + M) / S of greater than 2.3 contributes to a decrease in the concentration of slag, which also leads to a decrease in the concentration of the resulting reduced iron particles and to difficulties in obtaining a high yield of large particles of granular metallic iron, which is an object of the present invention. For the practical implementation of the production method according to the present invention from an economic point of view, large particles of granular metallic iron, which is the aim of the present invention, should be obtained with the highest possible yield even when the basicity of the slag (C + M) / S at the final stage is 2.3 or less.

Accordingly, the authors of the present invention as a result of intensive research have developed a method to prevent a decrease in the yield of granular metallic iron with a suitable particle size due to the increased basicity of the slag (C + M) / S. In other words, adding to the mixture of materials an appropriate amount of CaF ₂ -containing substance, for example fluorite, improves fluidity and also reduces the melting point of the resulting slag, thereby contributing to the concentration of slag, and also improving the concentration of reduced iron particles, thereby significantly increasing the yield of large particles granular metallic iron. It was found that the added above-mentioned CaF ₂ -containing substance should contain CaF ₂ in an amount of 0.2% or more in the entire composition of the slag, preferably 0.4% or more, in order to effectively realize the benefits obtained by using such CaF ₂ -containing substances on a practical scale.

More specifically, according to this embodiment, if the basicity of the slag (C + M) / S at the final stage is 1.7 or more, in particular more than 1.8, CaF _{2 is} added to a mixture of materials with a CaF ₂ content of 0.2% or more of the slag composition in such a way that the increased CaF ₂ content compensates for the loss of fluidity due to the increased basicity of the slag (C + M) / S, thereby ensuring the stable production of large particles of granular metallic iron in high yield.

It should be noted that the use of excess CaF ₂ causes too much fluidity of the resulting slag, which raises another problem, namely, that under, made of refractory material, is easily damaged. Accordingly, the concentration of CaF ₂ -containing substance is preferably reduced to 2% or less of the total slag composition, more preferably to 1.5% or less.

It should be noted that in the production method according to the present invention, the basicity (C + M) / S of the resulting slag and the MgO content are determined by the method described above, which is the most essential component of the present invention. On the other hand, while the carbon-containing material loaded in such a way as to be distributed over the hearth is not indispensable, the aforementioned carbon-containing material loading is preferable to more effectively improve the reduction potential in the furnace and, as a result, more effectively provide both advantages. such as a high yield of metallic iron and a decrease in its sulfur content. It should be noted that when using the aforementioned method for loading carbon-containing material, the carbon-containing powder material is preferably loaded so that it is distributed over the surface of the underlayer of about 2 mm in order to guarantee this advantage. Moreover, the carbon-containing material distributed over the hearth serves as a buffer between the mixture of raw materials and the hearth made of refractory material, in addition, it protects the hearth, thereby extending its service life.

It should be noted that if the carbon-containing material is distributed too thick over the hearth, the mixture of materials flows into the carbon-containing material distributed over the hearth, which can slow down the reduction of iron oxide. Accordingly, the thickness of the aforementioned carbon-containing material distributed over the hearth is preferably limited to 7.5 mm or less.

It should be noted that the form of the aforementioned carbon-containing material distributed over the hearth is not particularly limited, and a conventional coal or coke crushing device may be used, preferably configured to obtain a suitable grain size. It should be noted that when using coal, anthracite is preferred because of its low fluidity, low expansion and adhesion to the hearth.

Examples

Despite the specific description set forth below with reference to examples, the present invention is not limited to the examples presented here, on the contrary, if necessary, it can be subjected to appropriate modifications without violating the essence and scope of the attached claims in light of the above and the following descriptions, which are also included in the technical scope of the present invention.

Example 1

First of all, compacts are obtained from raw materials in the form of pellets from iron ore, used as substances containing iron oxide, while coal is used as a carbon-containing reducing agent, and additional material, such as limestone (CaCO ₃ ), dolomite (CaCO ₃ · MgCO ₃ ) or the like - to regulate the basicity of the slag, and if necessary, add a suitable amount of fluorite (CaF ₂ ) and, in addition, a small amount of wheat flour used as a binder.

It should be noted that, as shown in table 1, two types of iron ore are used - A and B. On the other hand, the composition of coal used as a carbon-containing reducing agent is presented in table 2.

table 2 The results of industrial analysis (wt.%) Elemental analysis (wt.%) Volatile component Total ash content Sulfur Phosphorus Total C H N Cl S Ash R ABOUT 19.90 8.6 0.53 0,029 28.5 81.77 4.33 1,64 0,03 0.53 8.04 0,029 3.63 The results of the analysis of the ash component (wt.%) Fe ₂ O ₃ Al ₂ O ₃ TiO ₂ Fe ₂ O ₃ CaO MgO Na ₂ O K ₂ O P ₂ O ₆ Other 49.44 34.68 1.84 4.78 2.72 1.01 0.48 2.09 0.76 2.2

The aforementioned raw material compacts are continuously fed into a small rotary hearth experimental reduction furnace for heating and reduction. The corresponding temperatures of the heating-reduction zone and cementing-melting zone are set at a level of from 1400 to 1470 ° C by heating with burners. The iron oxide contained in the raw material compact fed to the under furnace is subjected to solid reduction during its passage through the heating zone in the furnace over a cycle of about 10 to 16 minutes. The resulting reduced iron is subjected to carburization under the influence of the remaining carbon-containing substance at the last stage of reduction in a furnace with a reducing atmosphere, which leads to a decrease in the melting point and to a concentration of reduced iron. On the other hand, the resulting slag melts completely or partially, which also leads to a concentration of slag, thereby contributing to the separation of the molten granular metallic iron from the molten slag. Then, the obtained molten granular metallic iron and molten slag are cooled to a melting point or lower (specifically, cooled to a temperature of approximately 1100 ° C.) so as to solidify them at the final stage of a reducing atmosphere furnace, after which the granular metallic iron and slag are solid unload from the oven.

It should be noted that hematite ore, which is a typical iron ore, is used as iron ore (A). On the other hand, magnetite ore, which is also a typical iron ore, is used as iron ore (B). According to the present example, various types of raw compacts containing the aforementioned materials are subjected to heating and reduction at various slag basicities (C + M) / S at the final stage, with a maximum slag basicity of 1.8. The test results are presented in figure 5 and 6.

Figure 5 shows the test results using iron ore (A), i.e. hematite, with the horizontal axis representing the basicity (C + M) / S of the resulting slag, and the vertical axis representing the sulfur distribution coefficient (S) / [S], obtained on the basis of sulfur analysis by measuring the sulfur concentration in the obtained granular metallic iron and the resulting slag.

As is apparent from the results presented in FIG. 5, when using iron ore (A), i.e. hematite, as an iron oxide-containing substance, increased slag basicity (C + M) / S, in particular increased slag basicity (C + M) / S greater than 1.4, causes a rapid increase in sulfur distribution coefficient (S) / [S]. It should be noted that in Fig. 5, white circles represent test results when using only limestone as an agent for regulating slag basicity, and solid circles represent test results when using limestone and dolomite as an MgO-containing substance for regulating slag basicity (C + M ) / S.

Despite the fact that the results obtained depend on the brand of coal used, as is obvious from the test results, the preparation is generally preferably carried out while maintaining the distribution coefficient of sulfur (S) / [S] at 25 or more, more preferably 30 or more, with the aim of reducing the sulfur content in the obtained metal granular iron, preferably to a value of 0.05% or less, and more preferably 0.04% or less.

If the slag basicity (C + M) / S is 1.4 or more, the higher the slag basicity (C + M) / S, the higher the sulfur distribution coefficient (S) / [S]. In this case, it clearly follows from the drawing that the vigorous addition of an Mg-containing substance to the slag composition further increases the sulfur distribution coefficient (S) / [S] compared to the case when the Mg-containing substance is not used. It should be noted that in the case when the Mg-containing substance is not used, an increased slag basicity (C + M) / S of approximately 1.7 at the final stage causes an increase in the melting temperature of the slag, therefore, the concentration of molten slag is slower, which leads to a slowdown in the separation of reduced iron. As a result, a large number of small particles of granular metallic iron is formed, which makes it difficult to obtain large particles of granular metallic iron in high yield.

However, if the basicity of the slag (C + M) / S is 1.7 or more without an Mg-containing substance, the addition of a CaF ₂ -containing substance with a CaF ₂ content of 0.2% or more, preferably 0, 4% or more, of the composition of the slag, improves the fluidity of the slag, and also again reduces the melting point of the slag, providing large particles of granular metallic iron in high yield.

On the other hand, FIG. 6 presents test data using magnetite ore as an iron oxide-containing substance obtained as a result of testing in a manner analogous to the above method using hematite, the mechanism of which is generally the same as shown in FIG. However, in this example, an increased slag basicity (C + M) / S of 1.2 or more causes a rapid increase in the sulfur distribution coefficient (S) / [S]. The absence of a clear distinction between the test results in this example and the test results presented in the above figure 5 confirms that the test results in the case of using dolomite as an MgO-containing substance represented by solid circles show a significantly higher sulfur distribution coefficient (S ) / [S] compared with the test results when dolomite represented by white circles was not used. In other words, according to the test results when using magnetite ore as a substance containing iron oxide, the addition of MgO-containing substance as a whole provides the same advantage as when using hematite ore (A) as the above-described substance containing iron oxide.

As described above, in the reduction and melting method according to this embodiment, the MgO-containing substance is added to the raw material mixture in advance so that the basicity of the slag (C + M) / S is 1.3 or more, preferably 1.4 or more , at the final stage, providing a high level of desulfurization and thereby reducing the sulfur content in the granular metal iron to 0.05% or less, and more preferably 0.04% or less. This is presumably due to the fact that adding a suitable amount of MgO-containing substance lowers the melting point of the slag in the same way as adding fluorite, even when the CaF ₂ -containing substance is not added, providing improved separation of the reduced iron from the slag, as well as the concentration of both slag and reduced iron.

Example 2

An example is described below in accordance with which two types of pellet compacts are obtained, mainly made of hematite ore (A) and coal, as shown in Table 1 and Table 2 above, and further containing limestone or dolomite, then the pellets thus obtained are subjected to reduction and melting in a rotary hearth furnace with a reducing atmosphere. It should be noted that the pellets used from raw materials (a) and (b) have the composition shown in Table 3. Both pellets (a) and pellets (b) are obtained from hematite ore (A). It should be noted that no MgO-containing substance was added to the previous pellets (a). On the other hand, natural dolomite ore, serving as an MgO-containing substance, was added to the last pellets (b). When conducting these tests, the preparation is carried out at an atmosphere temperature in the furnace equal to 1450 ° C.

The results of the analysis of granular metallic iron and slag formed during the test, as well as the basicity of the slag (C + M) / S and the distribution coefficient of sulfur (S) / [S] are presented in table 4.

Table 3 View The composition of the raw material (wt.%) Iron ore Coal CaCO ₃ Dolomite Binder Pellet (a) 73.33 20.74 4.73 0 1,2 Pellet (b) 73,2 20.7 3.09 1.81 1,2 Table 4 Granular iron Slag (S) / [S] (C + M) / S [C] [S] Cao SiO ₂ MgO S Pellet (a) 4.03 0.059 46.46 28.82 2,5 1.351 22.75 1,699 Pellet (b) 4.12 0,035 40.26 28.68 8.81 1,588 45.03 1,711

As obviously follows from table 4, despite the fact that the pellet (a) was obtained when the slag basicity (C + M) / S within the range established according to the present invention, the slag has a low MgO content of 2.5% and is outside range in accordance with the present invention, since only CaCO ₃ , without dolomite, was added to the pellet, which is a compact from a mixture of raw materials. In this case, the sulfur distribution coefficient (S) / [S] is 22.75, not reaching the desired value of 25.0, which is the reason for the high sulfur content [S], equal to 0.059%, in granular metallic iron.

On the other hand, dolomite in an amount of 1.81% was added to the pellet (b) satisfying the conditions of the present invention, which provides a slag basicity (C + M) / S of 0.71, a high MgO content in the slag of 8.81%, and a very high sulfur distribution coefficient (S) / [S] of 45.03, thereby providing a very low sulfur content [S] of 0.035% in the resulting granular metallic iron.

As indicated above, the production method according to the present invention confirms that granular metallic iron can be obtained with a sulfur content [S] of 0.05% or less, more preferably 0.04% or less, by appropriately adjusting the amount of MgO-containing substances in the mixture of raw materials, thus ensuring the basicity of the slag (C + M) / S in the range from 1.3 to 2.3 at the final stage, and the MgO content in the slag in the range from 5 to 13%, which depends on the corresponding amounts of CaO , MgO and SiO ₂ contained in the mixture of materials.

Claims (9)

1. A method for producing granular metallic iron with a low sulfur content, in which a mixture of raw materials, including an iron oxide-containing substance and a carbon-containing reducing agent, is fed under a heated rolling hearth furnace with a reducing atmosphere, the raw material mixture is heated and iron oxide contained in the aforementioned is reduced mixtures by means of the aforementioned carbon-containing reducing agent, provide separation of the particles of the obtained metallic iron from the resulting slag, subjected to the obtained e metal iron is cooled to cure, after which granular metal iron is discharged, while the amounts of CaO-containing substance, MgO-containing substance and SiO ₂ -containing substance contained in the mixture are controlled to form slag basicity (CaO + MgO) / SiO ₂ , equal to from 1.3 to 2.3, while MgO is contained in the slag in the range from 5 to 13 wt.% Depending on the composition of the slag, determined by the amount of each of the substances: CaO, MgO and SiO ₂ contained in the raw material mixture . 2. The method according to claim 1, in which the MgO-containing substance is additionally mixed with said raw material mixture to obtain said slag basicity and MgO content. 3. The method according to claim 2, in which crude dolomite is used as the MgO-containing substance. 4. The method according to claim 1, in which a CaF ₂ -containing substance is additionally added to said raw material mixture. 5. The method according to claim 4, in which fluorite is used as said CaF ₂ -containing substance. 6. The method according to claim 4 or 5, in which said CaF ₂ -containing substance is contained in said raw material mixture in an amount of from 0.2 to 2 wt.%. 7. The method according to claim 1, in which the carbon-containing powder is loaded so that it is distributed over said hearth prior to loading said raw material mixture into a moving hearth furnace with a reducing atmosphere. 8. The method according to claim 7, in which the aforementioned carbon-containing powder is loaded so that it is distributed over the hearth with a layer of 2 mm or more thickness. 9. The method according to claim 1, in which the operating temperature from 1250 to 1550 ° C. is set in said heated hearth furnace with a reducing atmosphere.

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